1. Field of the Invention
The present invention relates to a pattern forming method.
2. Discussion of the Background
In the field of microfabrication represented by fabrication of IC chips, miniaturization of the design rules is rapidly progressing in order to achieve higher integration of the circuits. Development of a lithographic process enabling microfabrication in a stable manner has been actively pursued. However, since it has been difficult to form micro patterns of less than 45 nm with high precision by a general method of using a KrF or an ArF excimer laser, a method of using electron beams (EB) or extreme ultraviolet radiation (EUV) has been proposed.
The following various radiation-sensitive resin compositions have been proposed as positive-tone resists for electron beams or extreme ultraviolet radiation used for such ultra-microfabrication.
(1) Chemically-amplified radiation-sensitive resin composition comprising a polyhydroxystyrene resin partially protected by an acid-dissociable functional group (resin for KrF excimer), a novolak (resin for i lines), and an acid-dissociable group:
Various patent applications such as a composition containing a polyhydroxystyrene resin partially protected by an acetal group and an acid generator having well-balanced sensitivity and resolution (see JP-A-6-194842), a composition containing polyhydroxystyrene resin partially protected by various acid dissociable groups, an onium salt which generates a fluorine-containing aromatic sulfonic acid, and a fluorine-containing or silicon-containing surfactant (see JP-A-2000-187330), an onium salt having at least one electron attractive group (fluorine, a cyano group, a nitro group) as a substituent of a cation moiety (see JP-A-2001-075283), a resin having a disulfonyl group (see JP-A-2002-072483), a resin having N-oxyimidesulfonyl group (see JP-A-2002-107920), and the like have been disclosed.
Micro-pattern formation is said to be difficult when using a chemically amplified resist utilizing an effect of acid diffusion (see “Relation between spatial resolution and reaction mechanism of chemically amplified resists for electron beam lithography”, Journal of Vacuum Science & Technology B (USA), December, 2003, Vol. 21, No. 6, pp. 3149 to 3152).
(2) PMMA (polymethylmethacrylate) main chain cutting-type radiation-sensitive resin composition:
The resin composition exhibits excellent resolution.
Poly-t-butyl-α-chloromethylstyrene exhibiting excellent balance of resolution and sensitivity (JP-A-2000-147777) and a resin with an atom (N, O, S) which is easily cut by electron beams introduced into the resin terminal (JP-A-11-29612) have been disclosed.